Electronically abrupt borophene/organic lateral heterostructures and preparation thereof

ABSTRACT

A method of preparing a boron allotrope-organic lateral heterostructural article includes providing an article comprising a substrate comprising a portion thereof coupled to a boron allotrope comprising an elemental boron layer; generating an organic compound vapor from a solid organic compound source, said organic compound vapor having a higher enthalpy of adsorption on said substrate compared to enthalpy of adsorption on said boron allotrope; and contacting said organic compound vapor with said article to selectively deposit said organic compound on a substrate portion not coupled to said boron allotrope to provide a heterostructural article comprising said organic compound and said boron allotrope laterally adjacent one to the other and providing a lateral interface one with the other.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

This application is a divisional application of and claims the benefitof U.S. patent application Ser. No. 15/892,124, filed Feb. 8, 2018, nowallowed U.S. Pat. No. 10,550,003, which claims priority to and thebenefit of U.S. provisional patent application Ser. No. 62/499,938 filedFeb. 8, 2017, which are incorporated herein in their entireties byreference.

STATEMENT AS TO RIGHTS UNDER FEDERALLY-SPONSORED RESEARCH

This invention was made with government support under N00014-14-1-0669awarded by the Office of Naval Research, and DMR-1121262 awarded by theNational Science Foundation. The government has certain rights in theinvention.

FIELD OF THE INVENTION

The present invention relates generally to semiconductors, and moreparticularly to electronically abrupt borophene/organic lateralheterostructures, fabricating methods and applications of the same.

BACKGROUND OF THE INVENTION

The rapid ascent of graphene has driven extensive interest in additionalatomically thin elemental two-dimensional (2D) materials includingphosphorene, stanene, and most recently, borophene. (See, A. J. Mannix,X.-F. Zhou, B. Kiraly, J. D. Wood, D. Alducin, B. D. Myers, X. Liu, B.L. Fisher, U. Santiago, J. R. Guest, M. J. Yacaman, A. Ponce, A. R.Oganov, M. C. Hersam, N. P. Guisinger, Synthesis of borophenes:Anisotropic, two-dimensional boron polymorphs, Science 350, 1513-1516(2015)). Unlike the naturally layered structures of bulk graphite andblack phosphorus, boron exhibits significantly more complex and diversebulk structures due to the rich bonding configurations among boronatoms. Studies of atomically thin boron sheets (i.e., borophene)primarily relied on theoretical predictions until recent studiesexperimentally demonstrated borophene synthesis on Ag(111) substrates.These experimental studies have confirmed theoretical predictions thatborophene is a 2D metal and can adopt multiple structurally distinctphases as a function of processing conditions.

As an emerging 2D material, borophene has thus far only been studied inisolation, whereas nearly all technological applications will requirethe integration of borophene with other materials. Of particularinterest are electronically abrupt lateral heterostructures, which havebeen widely explored in other 2D materials due to their novel electronicproperties. For example, atomically well-defined lateralheterostructures between graphene and hexagonal boron nitride haverevealed spatially confined boundary states with scanning tunnelingspectroscopy (STS). It should be noted, however, that methods forexperimentally realizing atomically clean and abrupt lateralheterojunctions remain challenging for many 2D material systems. Forexample, the growth front of the first 2D material can be easilycontaminated, which can disrupt the subsequent growth of the second 2Dmaterial and/or lead to ill-defined interfacial regions. Alloying andintermixing during the growth of 2D material lateral heterostructuresalso prevents abrupt interfaces.

SUMMARY OF THE INVENTION

In light of the foregoing, it can be an object of the present inventionto provide lateral heterostructures comprising borophene and/or relatedboron allotropes and/or method(s) for a preparation thereof, therebyovercoming various deficiencies and shortcomings of the prior art,including those outlined above. It will be understood by those skilledin the art that one or more aspects of this invention can meet certainobjectives, while one or more other aspects can meet certain otherobjectives. Each objective may not apply equally, in all its respects,to every aspect of this invention. As such, the following objects can beviewed in the alternative with respect to any one aspect of thisinvention.

It can be an object of the present invention to provide articles ofmanufacture comprising lateral heterostructures comprising anatomically-thin boron allotrope, for instance and without limitation, atwo-dimensional boron sheet (i.e., borophene) and another material.

It can be another object of the present invention to provide suchheterostructures without alloying or boron compound formation.

It can be another object of the present invention, alone or inconjunction with one or more of the preceding objectives, to provide awell-defined lateral interface of boron with another such material atnanometric molecular length scales.

Other objects, features, benefits and advantages of the presentinvention will be apparent from this summary and the followingdescriptions of various preferred embodiments, and will be readilyapparent to those skilled in the art having knowledge of elementalboron, nano-dimensioned allotropes thereof, related heterostructuresand/or method(s) of preparation. Such objects, features, benefits andadvantages will be apparent from the above as taken into conjunctionwith the accompanying examples, data, figures and all reasonableinferences to be drawn therefrom, alone or with consideration of thereferences incorporated herein.

In part, the present invention can be directed to an article comprisinga substrate; a boron allotrope comprising an elemental boron layer ofboron atoms comprising a boron atomic thickness dimension; and anorganic compound layer, said boron allotrope layer and said organiccompound layer on and/or coupled to said substrate, laterally adjacentone to the other and providing a lateral interface one with the other.Without limitation, such an allotrope can be two-dimensional boropheneand, independently, such an organic compound can be a polycyclicaromatic compound comprising one or more moieties affording such acompound a capability for intermolecular hydrogen bonding, such a moietyincluding but not limited to one or more carboxylic acid anhydridemoieties, such polycyclic aromatic compounds and moieties thereof aswould be understood by those skilled in the art and made aware of thisinvention. As a separate consideration, such a substrate can comprise anoble metal.

In certain non-limiting embodiments, such an organic compound cancomprise a self-assembly product of perylene-3,4,9,10-tetracarboxylicdianhydride (PTCDA). As an independent consideration, such a substratecan be silver. Certain such embodiments can comprise a single crystalAg(111). In certain other non-limiting embodiments, such a boronallotrope can comprise a homogeneous boron phase. In certain suchembodiments, such a boron allotrope can be metallic and, independently,such an organic compound can be semiconducting. Without limitation, suchan organic compound can comprise a self-assembly product of PTCDA.

Regardless, without limitation, such an article can comprise such aboron allotrope substantially absent such an organic compound thereon.As can relate thereto, such a lateral interface can be characterized bycomplete structural and/or electronic transition from such a boronallotrope to such an organic compound layer over the nanometric lengthscale of such an organic compound.

In part, the present invention can also be directed to an articlecomprising a silver substrate; a metallic boron allotrope comprising anelemental boron layer of boron atoms comprising a boron atomic thicknessdimension; and a semiconducting organic compound monolayer comprising aself-assembly product of PTCDA, such boron allotrope and organiccompound layers on and/or coupled to such a substrate, laterallyadjacent one to the other and providing a non-covalent lateral interfaceone with the other. In certain non-limiting embodiments, such asubstrate can comprise single crystal Ag(111). In certain suchembodiments, such a boron allotrope can comprise a homogeneous boronphase.

In part, the present invention can also be directed to the preparationand/or the self-assembly of lateral heterostructures comprising a boronallotrope and/or a borophene and an organic material such as but notlimited to PTCDA. Accordingly, such a method of preparing such a lateralheterostructural article can comprise providing an article comprising asubstrate comprising a portion thereof coupled to a boron allotropecomprising an elemental boron layer; generating an organic compoundvapor from a solid organic compound source, such an organic compoundvapor having a higher enthalpy of adsorption on such a substratecompared to enthalpy of adsorption on such a boron allotrope; andcontacting such an organic compound vapor with such an article toselectively deposit such an organic compound on a substrate portion notcoupled to such a boron allotrope, to provide a heterostructural articlecomprising such an organic compound and such a boron allotrope laterallyadjacent one to the other and providing a lateral interface one with theother. Without limitation, such deposition can provide completestructural and/or electronic transition from such a boron allotrope toan organic compound layer over the nanometric length scale of such anorganic compound. As can relate thereto, such a method can utilizeintermolecular hydrogen bonding to prepare such a lateralheterostructural article. Such a method can be as described above, withgeneration of an organic compound vapor from a solid organic compoundsource capable of lateral intermolecular hydrogen bonding, toselectively deposit such an organic compound on a substrate portion notcoupled to such a boron allotrope.

Without limitation to any one theory or mode of operation, such lateralheterostructures can spontaneously form, for instance, upon depositionof PTCDA on submonolayer borophene on Ag(111) substrates due to thehigher adsorption enthalpy of PTCDA on Ag(111) and lateral hydrogenbonding among PTCDA molecules, as can be demonstrated by moleculardynamics simulations. In situ X-ray photoelectron spectroscopy confirmsthe non-covalent interaction between borophene and PTCDA, whilemolecular-resolution ultrahigh vacuum scanning tunneling microscopy andspectroscopy reveal an electronically abrupt interface at theborophene/PTCDA lateral heterostructure interface.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1D show homogeneous-phase borophene. (A) Schematic of borophenegrowth on Ag(111) thin film on mica. Inset: atomic resolution STM imageof the Ag(111) surface (Vs=0.01 V, It=100 pA). (B) STM digital image oftriangular borophene islands on Ag(111). Under these imaging conditions(V_(s)=1.2 V, I_(t)=160 pA), the borophene islands appear asdepressions. (C) In situ XPS spectra of the B is core-level on pristineborophene (top) and Ag 3d core-levels (vertically offset) before andafter borophene growth (bottom). (D) Ex-situ AFM digital image ofborophene/Ag(111) with borophene islands appearing as protrusions.

FIGS. 2A-2F show carpet-mode growth of homogeneous phase borophene. (A)Scanning tunneling microscopy (STM) digital image of borophene islandscovering Ag(111) step edges (V_(b)=1.5 V, I_(t)=50 pA). (B) Atomicresolution STM digital image of homogeneous-phase borophene growing on aAg terrace (lower square in (A), V_(b)=−0.2 V, I_(t)=50 pA). (C) STMdigital image of homogeneous-phase borophene continuously growing over aAg(111) step edge (upper square in (A), V_(b)=−0.2 V, I_(t)=50 pA). Thisimage confirms that homogeneous-phase borophene adopts carpet-modegrowth as has been previously observed for striped-phase borophene.(D-F) Additional large-scale STM digital images of homogeneous-phaseborophene growing on and continuously across Ag(111) terraces. Theborophene islands in (E) and (F) are outlined by white dashed lines. Agsteps are discontinuous when they cross borophene islands, presumablydue to migration of the Ag terraces during borophene growth at elevatedtemperatures ((D): V_(b)=0.8 V, I_(t)=50 pA, (E): V_(b)=1.2 V, I_(t)=50pA, (F): V_(b)=0.91 V, /_(t)=50 pA).

FIGS. 3A-3B show X-ray photoelectron spectra (XPS) of Ag 3d and O 1score-levels. (A) Ag 3d core-level XPS spectra of clean Ag, borophene/Ag,and PTCDA/borophene/Ag (Ag 3d_(5/2): 368.2 eV, Ag 3d_(3/2): 374.2 eV,plasma loss peak of Ag 3d_(5/2): 372.0 eV. The full widths at halfmaximum for all three Ag 3d_(5/2) peaks are 0.68 eV. Since the amount ofadventitious carbon is small in these samples, all three spectra werecharge-corrected by the same amount as determined by the Ag 3d_(5/2)peak position of clean Ag(111). No detectable shift of the peakpositions is observed after borophene growth. Following the formation ofborophene/PTCDA lateral heterostructures, the Ag 3d_(5/2) is upshiftedby 0.04 eV, which is negligible compared to the instrumental energyresolution of 0.6 eV, but could be consistent with a higher bindingenergy due to electron transfer from Ag to PTCDA as discussed below. (B)O is core-level XPS spectra of clean Ag, borophene/Ag, andPTCDA/borophene/Ag (vertically offset). Following PTCDA deposition, twosub-peaks at 530.6 eV and 533.0 eV arise from the C—O—C and C=0 bonds inPTCDA. The XPS spectra of clean Ag(111) and borophene/Ag(111) show noevidence of oxygen.

FIGS. 4A-4G show structural and electronic properties ofhomogeneous-phase borophene. (A) Atomic resolution STM digital image ofhomogeneous-phase borophene showing the brick-wall structure (V_(s)=−1.2V, I_(t)=2.4 nA). Inset: fast Fourier transform (FFT) of the image. Thescale bar is 2 nm⁻¹. (B) STM digital image showing a borophene 60° grainboundary (V_(s)=−0.15 V, I_(t)=3.0 nA). (C) STM digital images showingline defects in borophene. Brick-wall patterns and the line defects arehighlighted with ovals and arrows, respectively, in the bottom image(V_(s)=−1.1 V, I_(t)=500 pA). (D) STM digital image showing alignedpoint defects along a line defect as indicated by the upper and lowestarrows, respectively (V_(s)=−60 mV, I_(t)=4.3 nA). (E) Current-voltageand (F) differential tunneling conductance spectra of Ag(111) andborophene. (G) STS digital maps of borophene on Ag(111) at sample biasesof −0.2 V and 0.1 V.

FIGS. 5A-5C show bias-dependent atomic resolution images ofhomogeneous-phase borophene. STM digital images biasing conditions are(A): V_(b)=−1.2 V, I_(t)=2.36 nA, (B): V_(b)=−0.19 V, L=2.36 nA, (C):V_(b)=−0.27 V, I_(t)=1.45 nA. The arrows indicate the row directions(i.e., the b direction in FIG. 4A). Insets: fast Fourier transforms ofthe corresponding real space images. The scale bars are 2 nm⁻¹. Thewhite circles indicate the frequency-space points that correspond to theperiodic row patterns. Although the brick-wall type structure in (A) iscommonly observed, finer structure details dominate the contrast atcertain scanning conditions, leading to the brick-wall pattern not beingdiscernable, as shown in (B) and (C).

FIGS. 6A-6G show borophene/PTCDA lateral heterostructure. (A)Large-scale STM digital image of a borophene/PTCDA lateralheterostructure and the cross-sectional profile along the white dashedline (V_(s)=−1.7 V, I_(t)=90 pA). Borophene to PTCDA step edges, Ag toPTCDA step edges, and Ag atomic step edges under PTCDA and borophenecorrespond to the cross-sectional profile, below, and are indicated bythe respective arrows. Inset: PTCDA molecule structure. (B) Schematic ofa borophene/PTCDA lateral heterostructure. (C) Unit cell schematic ofthe PTCDA herringbone structure. (D) STM digital image of aborophene/PTCDA lateral heterostructure with the upper, middle and lowerboxes indicating regions of PTCDA, borophene, and Ag, respectively(V_(s)=−1.1 V, I_(t)=90 pA). (E to G) STM digital images of the squareregions indicated in (D). The pair of arrows indicate the latticeorientations of borophene and Ag(111) ((E): V_(s)=−0.45 V, I_(t).=140pA, (F): V_(s)=−1.1 V, I_(t)=500 pA, (G): V_(s)=−70 mV, I_(t)=6.1 nA).

FIGS. 7A-7B show additional atomic resolution image of borophene. (A)STM digital image of the borophene/PTCDA lateral heterostructure in FIG.6A (V_(b)=−1.7 V, I_(t)=90 pA). (B) Atomic resolution digital image ofthe borophene region indicated by the square in (A), supporting theassignment of borophene in FIG. 6A. Line and point defects are seen atthe top and bottom parts of the image (V_(b)=0.11 V, I_(t)=2.54 nA).

FIGS. 8A-8C show STM digital images of growth of PTCDA across variousinterfaces. (A) Borophene/PTCDA interface. The PTCDA molecules aremobile at the interface due to the perturbation of STM tip and the weakinteraction between PTCDA and borophene (V_(b)=−0.85 V, I_(t)=60 pA).(B) Carpet-mode growth of PTCDA across a Ag step edge (V_(b)=−0.85 V,I_(t)=60 pA). (C) The edge of a PTCDA island on Ag(111) (V_(b)=−1.07 V,I_(t)=50 pA).

FIGS. 9A-9C show additional digital images (A and C) of PTCDA/borophenelateral heterostructures. (A) Large-scale STM digital image of boropheneislands surrounded by PTCDA monolayers (V_(b)=−1.6 V, I_(t)=50 pA). (B)The cross-sectional profile along the white dashed line in (A), whichreveals the 0.7 A apparent step height from borophene to Ag(111). (C)The black arrows indicate PTCDA molecules being dragged along the slowscan direction (top to bottom) on borophene, which is consistent with aweak interaction between PTCDA and borophene (V_(b)=−1.4 V, I_(t)=50pA).

FIG. 10 shows a design of a coarse-grained model for PTCDA. The designis based upon the hydrogen bonding network (black dashed lines) and unitcell (dashed rectangle) of a self-assembled herringbone lattice.

FIGS. 11A-11D show molecular dynamics simulation results. (A) ΔG(z),ΔH(z), TΔS(z) as a function of center-of-mass distance z to thehomogeneous substrate of a single PTCDA molecule with ΔH_(ads)=10k_(B)T. (B) ΔG_(ads) and probability ratio of finding a molecule beyondand within a threshold z₀=5.635 Å from the substrate, as a function ofΔH_(ads). (C) Surface coverage as a function of ΔH_(ads). Inset:simulation snapshots of PTCDA adsorption and self-assembly onhomogeneous Ag(111) substrates at different ΔHads. (D) Self-assembledstructure of PTCDA on heterogeneous borophene/Ag(111) substrates withΔH_(ads,B)=10 k_(B)T, 16 k_(B)T, 18 k_(B)T, and 22 k_(B)T.

FIG. 12 show entropy variation ΔS(z) of a single PTCDA molecule as afunction of logarithmic distance ln(z−z_(min)) to a homogeneoussubstrate. z_(min) is the distance at which the central bead of thePCTDA molecule and a Ag atom are touching. When a PTCDA molecule is inclose proximity to the substrate, ΔS(z) decreases logarithmically withsurface separation.

FIG. 13 shows probability ratio from thermodynamic integration andsingle-molecule simulation as a function of threshold z₀ at ΔH_(ads)=10k_(B)T. The result from thermodynamic integration is obtained byintegrating ΔG(z),

$\frac{P\left( {z > z_{0}} \right)}{P\left( {z < z_{0}} \right)} = \frac{\int_{z_{0}}^{z_{\max}}{e^{{- \Delta}\;{G{(z)}}}{dz}}}{\int_{z_{\min}}^{z_{0}}{e^{{- \Delta}\;{G{(z)}}}{dz}}}$where z_(min) is the distance at which the central bead of the PCTDAmolecule and a Ag atom are touching and z_(max) is the top of thesimulation cell. The single-molecule simulation results are obtained bydirectly sampling the position of a single molecule in a canonical MDsimulation. The agreement between the results obtained by directsampling and thermodynamic integration confirms the calculation ofΔG(z).

FIGS. 14A-14B show additional simulated adsorption of PTCDA onborophene/Ag(111). Self-assembled structure of PTCDA on heterogeneousborophene/Ag(111) substrates with (A) ΔH_(ads,Ag)=18 k_(B)T,ΔH_(ads,B)=10 k_(B)T, and (B) ΔH_(ads,Ag)=18 k_(B)T, ΔH_(ads,B)=16k_(B)T. The fact that no PTCDA adsorption is seen in (A) but in (B)indicates that the required adsorption enthalpy differential for PTCDAon Ag(111) and borophene is between 2 and 8 k_(B)T for fully selectiveadsorption of PTCDA on Ag(111).

FIGS. 15A-15F show spectroscopic properties of the borophene/PTCDAlateral heterostructure. (A) In situ XPS spectra of the B is core-level,and (B) C is core-level before and after the formation of theborophene/PTCDA lateral heterostructure. (C) Differential tunnelingconductance spectra of Ag(111), borophene, and PTCDA. (D) STS digitalmap of a borophene/PTCDA lateral heterostructure overlaid on athree-dimensionally rendered STM topography image (V_(s)=−1 V, I_(t)=90pA). (E) Spatially resolved STS spectra across the interfaces (STMdigital images) of borophene/Ag, and (F) borophene/PTCDA. The verticalblack lines in (E) and (F) indicate the positions of the Ag surfacestate feature and the LUM0+1 orbital of PTCDA far from the borophene/Agand borophene/PTCDA interfaces, respectively.

FIG. 16 show C is core-level XPS spectrum of a clean Ag (111) surface. Atrace amount of carbon is present (284.5 eV), likely due to adventitiouscarbon in the ultra-high vacuum chamber.

FIGS. 17A-17E show STM digital images of self-assembled PTCDA onAg(111). (A) A large area of defect-free PTCDA monolayer showing theherringbone structure across a Ag(111) step edge (V_(b)=−0.71 V,I_(t)=50 pA). (B) Point defects (V_(b)=−1.07 V, I_(t)=50 pA) and (C)line defects in PTCDA monolayers as indicated by the white arrows(V_(b)=−1.75 V, I_(t)=140 pA). (D) STM digital image of PTCDA imaged atsample bias of −0.8 V and (E) 0.6 V showing different molecular andsub-molecular contrast.

DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS

Relating to one or more non-limiting embodiments thereof, this inventioncan be illustrated by the first experimental demonstration andcharacterization of a boron allotrope and/or borophene lateralheterostructure with a representative organic material, the molecularsemiconductor perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA). Inaccordance with broader aspects of this invention, submonolayerhomogeneous-phase borophene is initially grown on Ag(111) on micasubstrates by electron-beam evaporation of a pure boron source,resulting in atomically pristine 2D boron sheets as confirmed by in situX-ray photoelectron spectroscopy (XPS). Subsequent deposition of PTCDAresults in preferential assembly on Ag(111), ultimately resulting in thepresence of dense and well-ordered PTCDA monolayers that form lateralheterostructures with the borophene flakes. PTCDA is known toself-assemble on a variety of substrates including metals, semimetals,semiconductors, oxides, and salt crystals. The fact that PTCDA does notself-assemble on borophene is thus unexpected, but leads to thedesirable formation of lateral heterostructures with borophene.

It has been reported in the literature that the electronic properties ofself-assembled monolayers can be tuned by neighboring materials. Inparticular, the noncovalent interaction of PTCDA with silver substratesleads to a delocalized 2D band state with a parabolic dispersion. Itshould also be noted that noncovalent van der Waals interactions areprevalent in electronic devices based on 2D and mixed-dimensionalheterostructures. For example, van der Waals coupled organic lateralheterostructures have been demonstrated as gate-tunable p-n diodes. Ithas also been reported that van der Waals coupled electronic states playan important role in determining the electronic structure and opticalproperties of double-walled carbon nanotubes. For the case of boropheneand PTCDA, in situ XPS verifies the absence of covalent bonding betweenborophene and PTCDA since the B is peak remains virtually unchangedfollowing the formation of borophene/PTCDA lateral heterostructures.Using molecular dynamics (MD) simulations, these observations areconsistent with a lower adsorption enthalpy of PTCDA on borophene andthe formation of a hydrogen bonding network between adsorbed PTCDAmolecules. Ultrahigh vacuum (UHV) scanning tunneling microscopy (STM)and STS measurements further show that these lateral borophene/PTCDAheterostructures are electronically abrupt at the molecular-scale. Inaddition to elucidating the unique chemistry of borophene, this work hasclear implications for borophene-based nanoelectronics.

Homogeneous-Phase Borophene:

The growth of borophene is schematically shown in FIG. 1A, where a boronflux created by electron-beam evaporation of a pure boron rod isdirected toward a Ag(111) thin film (˜300 nm thick) on mica substrate inUHV. The inset shows an atomic resolution STM image of the atomicallyclean Ag(111) surface preceding boron deposition. By maintaining thesubstrate at a temperature of −480° C., pure homogeneous-phase borophene(i.e., the common phase realized in the initial experimental reports ofborophene) is realized with surface coverage controlled by thedeposition duration. The STM image in FIG. 1B shows a representativemorphology of the resulting borophene growth both on and acrossatomically flat Ag(111) terraces. Atomic-scale STM imaging indicates acarpet-mode growth of homogeneous-phase borophene (FIG. 2), which waspreviously observed for striped-phase borophene. Due to the convolutionof electronic and physical structure in STM imaging, the boropheneislands appear as depressions at these STM imaging conditions, which isconsistent with previous reports. Furthermore, the borophene islandsadopt elongated or truncated triangular shapes with aligned edges, whichsuggests registry between borophene and the underlying Ag(111)substrate.

The chemical integrity of the as-grown borophene is probed by in situXPS, as shown in FIG. 1C. The B is core-level spectrum (top) shows aclear pristine boron peak (30) at −188 eV with no peaks observed athigher binding energies of −192 eV, which would otherwise correspond tooxidized boron. The pristine nature of borophene is further confirmed bythe absence of an oxygen peak in the 0 is core-level spectrum (FIG. 3).The Ag 3d core-level spectra (FIG. 1C, bottom) before and afterborophene growth reveal no detectable peak splitting, shifting, orbroadening, which suggests the absence of B—Ag alloying and thus theformation of chemically distinct 2D boron layers (FIG. 3). FIG. 1D showsan ex situ atomic force microscopy (AFM) image of borophene after beingexposed to air for ˜20 min. Triangular-shaped protrusions indicate thatthe borophene islands are topographically protruding above the Agsurface. The particles observed in the AFM image likely result fromboron particles during deposition, ambient-induced contamination, or Agoxidation.

Atomic-scale STM and STS characterization of borophene are provided inFIG. 4. The brick-wall-like structure of homogeneous-phase borophene isshown in FIG. 4A with the inset providing the fast Fourier transform(FFT). The measured inter-row distances are 4.5 Å and 8.2 Å in thelabeled a and b directions, which is consistent with previous reports.Although this brick-wall structure has been observed previously,additional atomic-scale contrast is observed at other bias conditions(FIG. 5). A 60° grain boundary of borophene is shown in FIG. 4B, furthersuggesting that the six-fold symmetry of the Ag(111) substrate templatesborophene growth. In addition to grain boundaries, another type offrequently observed one-dimensional defect is provided in FIG. 4C. Inthe bottom image, the brick-wall patterns and the line defects arehighlighted with ovals and arrows, respectively. The line defects areparallel and running along the b direction. Aligned point defects (upperarrows) are also found along these line defects (lowest arrow) as shownin FIG. 4D. The existence of these defects may provide strain relaxationthat helps accommodate the lattice mismatch between borophene andAg(111).

The electronic properties of homogeneous-phase borophene are furtherinterrogated with STS. FIG. 4E shows the current-voltage (I-V)measurements on both borophene and Ag(111), revealing the metallicbehavior of borophene. The differential tunneling conductance curves ofAg(111) and borophene are provided in FIG. 4F. Borophene exhibits anearly constant density of states (DOS) at small positive sample bias,whereas Ag(111) shows a feature that is consistent with literaturereports of the known surface state starting below the Fermi level. Theseelectronic differences are further demonstrated in FIG. 4G, where STSmapping over a borophene island at two different biases (−0.2 V and 0.1V) produces inverted contrast. STS maps over a continuous range ofsample biases between −0.3 V and 0.7 V are also available.

Self-Assembly of Borophene/PTCDA Lateral Heterostructures:

The deposition of PTCDA is achieved by thermally evaporating PTCDAmolecules from an alumina-coated crucible. Fine-tuning of theevaporation temperature and duration allows precise, layer-by-layergrowth of lateral hydrogen-bonded, self-assembled PTCDA on Ag(111). FIG.6A shows a large-scale STM image following PTCDA deposition onto asubmonolayer borophene on Ag(111) substrate. The large triangular-shapeddomain at the lower half of the image is a bare borophene islandsurrounded by a PTCDA monolayer and a small patch of clean Ag(111).Atomic resolution imaging of this borophene island (FIG. 7) confirms theabsence of PTCDA on the borophene surface.

The preferential assembly of PTCDA on Ag(111) compared to boropheneleads to the spontaneous formation of borophene/PTCDA lateralheterostructures. Due to the presence of steps in the underlying Ag(111)substrate, the geometry of the borophene/PTCDA lateral heterostructureis better understood through the cross-sectional profile (lower 6A)taken along the white dashed line (upper FIG. 6A), where each stepheight is labeled and indicated on the STM image by a correspondingarrow. The measured step heights of 2.4 Å across the PTCDA layer andborophene region correspond to a single atomic step height on Ag(111)(2.36 Å) as a result of the carpet-mode growth of PTCDA and boropheneover Ag step edges (FIGS. 2 and 8). The apparent step height of 2.3 Åfrom borophene to monolayer PTCDA is explained by the sum of the 0.7 Åstep height from borophene to Ag (111) (FIG. 9) and the 1.6 Å stepheight from Ag(111) to monolayer PTCDA. Therefore, the borophene/PTCDAlateral heterostructure consists of borophene laterally interfacing witha monolayer of self-assembled PTCDA on Ag(111) as shown schematically inFIG. 6B.

The self-assembly motif adopted by PTCDA on Ag(111) is the well-knownherringbone structure. FIG. 6C shows the unit cell of this structure,which is more directly observed in FIGS. 6D-6E. In particular, theupper, middle and lower squares in FIG. 6D highlight regions of PTCDA,borophene, and bare Ag, respectively. The zoomed-in STM images of eachregion are shown in FIG. 6E-6G, with the unit cell of PTCDAschematically overlaid in FIG. 6E. The relative lattice orientation ofhomogeneous-phase borophene and Ag(111) is denoted by the pairs ofarrows in FIGS. 6F-6G, which are parallel to each other and thusindicate registry between the two materials. This apparent registry isconsistent with the aligned triangular domains in FIG. 1B and theformation of 60° grain boundaries in FIG. 4B as noted above.

Molecular Dynamics Modeling:

To explore the effect of competing adsorption on the self-assembly ofmolecules on heterogeneous substrates, MD simulations were employed at afixed temperature T=300 K, which matches the experimental conditions.With large-scale collective effects that are not accessible through abinitio calculations, the PTCDA molecules were reduced to acoarse-grained representation (FIG. 10) capable of forming lateralhydrogen bonds as well as adsorption on the substrate. The Ag(111)substrate is represented as a hexagonally close-packed lattice, withinter-atomic spacing 2.898 Å. The excluded-volume interactions aremodeled with shifted-truncated Lennard-Jones (11) potentials and theattractions are represented by LJ potentials. (Without limitation to anyone theory or mode of operation, modeling studies were undertaken, asoutlined, the details of which are described more fully in the Examples,below.) Whereas the hydrogen bonding strength is kept fixed, theenthalpy of adsorption per molecule, ΔH_(ads), which can be defined asthe magnitude of the relative enthalpy ΔH(z)=H(z)−H(∞) upon adsorptionat z=z_(G), was systematically varied. The relative Gibbs free energyΔG(z) and entropy ΔS(z) are similarly defined. Here, z is the distancefrom the substrate and z_(G) is the position where ΔG(z) takes itsminimum. To set the scale of ΔH_(ads), the loss of entropy uponadsorption of a single coarse-grained PTCDA molecule via thermodynamicintegration was first quantified (see, Example 5). As shown in FIG. 11A,at ΔH_(ads)=10 k_(B)T, a Gibbs free energy of adsorption ΔG_(ads) ofapproximately 4 k_(B)T is found, implying an entropy loss ˜6 k_(B) for afully adsorbed PTCDA molecule. The functional form of the entropy loss(namely, logarithmic in surface separation z−z_(G)) can be rationalizedthrough estimation of the loss in degrees of freedom upon adsorption(FIG. 12).

To confirm the calculation of ΔG(z), the probability of finding a singlemolecule within a certain distance from the substrate was probed.Specifically, for a threshold z_(o)=5.635 Å, a ratioP(z>z_(o))/P(z>z_(o)) 10.99 is found, in relatively good agreement withthe value 11.76 computed by integration of ΔG(z) (see FIG. 13 andExample 5). As ΔH_(ads) is increased from 10 k_(B)T to 16 k_(B)T and 22k_(B)T, ΔG_(ads) increases accordingly, and the probability of finding asingle PTCDA molecule near the surface is greatly enhanced (FIG. 11B).Whereas this follows immediately from the Boltzmann distribution, thesituation is more subtle if upon adsorption molecules interact laterallyand form a regular surface packing. Thus, self-assembly of PTCDAmolecules on a homogeneous Ag(111) substrate is examined as a functionof ΔH_(ads). For molecular adsorption enthalpies of 10 k_(B)T and 16k_(B)T, only moderate adsorption levels (FIG. 11C) are found, asexpected from the significant entropy loss upon adsorption. As ΔH_(ads)is increased to 18 k_(B)T, significant surface coverage is observed,with the adsorbed molecules arranged in the herringbone structure foundexperimentally in FIG. 6D-6E (inset of FIG. 11C). Increase of ΔH_(ads)to 22 k_(B)T and 38 k_(B)T does not lead to an appreciable change, butat even higher adsorption enthalpy (60 k_(B)T), a large number ofdefects are observed. It is noted that these adsorption enthalpiesleading to almost full surface coverage are within the range found indensity functional theory calculations (0.5-3 eV), and ΔH_(ads,Ag)=38k_(B)T is employed for the study of competing adsorption onborophene/Ag(111) surfaces. The abrupt increase in surface coverage as afunction of ΔH_(ads) is consistent with a first-order transition (FIG.11C).

To model the formation of lateral heterostructures on heterogeneoussubstrates of borophene grown on Ag(111), a second hexagonallyclose-packed lattice layer partially covering the original substrate isadded, to represent a borophene island (islands in FIG. 11D). Within thecontext of this coarse-grained model and considering that the atomicstructure of homogeneous-phase borophene is not well-established, thesame structure is chosen for the borophene island, to focus on theenergy barriers posed by domain edges and, most importantly, the role ofcompetitive binding. The latter is investigated by fixing ΔH_(ads,Ag) onAg(111) at 38 k_(B)T per molecule, then systematically varying theadsorption enthalpy on borophene, ΔH_(ads,B). As illustrated in FIG.11D, PTCDA molecules self-assemble on Ag(111) in all cases and graduallyadsorb and self-assemble on the borophene island as ΔH_(ads,B) isincreased. As expected, negligible adsorption takes place for ΔH_(ads,B)below 18 k_(B)T. However, even for ΔH_(ads,B)=18 k_(B)T, full coverageand self-assembly are found for a homogeneous substrate, and low,unordered coverage occurs on the borophene, owing to the competingadsorption by the Ag(111) substrate. Moreover, the energy barrier at theboundary causes the coverage on Ag(111) to terminate abruptly at theedge of the borophene island. Only when ΔH_(ads,B) is increased to 22k_(B)T, self-assembly occurs on both substrates. It is important to notethat for the study of competitive binding the total number of PTCDAmolecules in the system must be limited to the amount needed for fullcoverage of the Ag(111). Since the present model does not permitmulti-layer adsorption, at higher PTCDA availability adsorption onborophene will occur as well once the Ag(111) is fully covered andΔH_(ads,B) is increased to a sufficiently high level. Interestingly, thehydrogen bonding responsible for the formation of the herringbonestructure plays a role in suppressing accumulation of PTCDA on the lessadsorbing substrate, since at dilute coverage molecules cannot formlateral hydrogen bonds (FIG. 11D, second and third panel). Therefore,within the limitations of the coarse-grained model and the assumptionthat differences in adsorption are not governed by surface geometry, itis found that a PTCDA adsorption enthalpy on borophene of less than ˜16k_(B)T (0.4 eV), combined with a differential in PTCDA adsorptionenthalpy between Ag(111) and borophene of several k_(B)T (−0.1 eV, FIG.14), is sufficient to fully explain the experimental observations.

Spectroscopy of Borophene/PTCDA Lateral Heterostructures:

FIG. 15A displays in situ XPS spectra of borophene before and afterPTCDA deposition. Consistent with the absence of PTCDA on the borophenesurface, the B is core-level peak is essentially unchanged followingPTCDA deposition with the exception of a small downshift (<0.2 eV) tolower binding energy. On the other hand, in response to the PTCDAmonolayer on the surrounding Ag(111) surface, the C is spectrum in FIG.15B shows a significant increase in peak intensity, where the twosub-peaks at 284.3 eV and 287.6 eV correspond to the perylene core andcarbonyl groups in PTCDA. The small presence of C preceding PTCDAdeposition can be attributed to trace amounts of adventitious carbon forAg on mica (FIG. 16). In FIG. 6A, relatively few individual PTCDAmolecules are present atop borophene primarily at points that align withunderlying Ag step edges. Charge transfer between metallic borophene andthese sparsely adsorbed PTCDA molecules, as well as the PTCDA moleculesat the borophene/PTCDA lateral heterojunction interface, presumablyleads to the minor peak shift in the B is core-level spectrum.Consistent with this interpretation, charge transfer between PTCDA andconventional metallic substrates, including Ag, results in the lowestunoccupied molecular orbital (LUMO) shifting below the Fermi level.

To further probe electronic interactions between borophene and PTCDA,STS characterization is performed on the borophene/PTCDA lateralheterostructure substrate. Specifically, STS spectra are presented inFIG. 15C for clean Ag(111), borophene, and monolayer PTCDA. Thelineshape and features for the PTCDA STS spectrum agree well withliterature precedent for the highest occupied molecular orbital (HOMO,−1.7 eV), LUMO (−0.3 eV), and LUM0+1 (0.8 eV). FIG. 15D shows a renderedthree-dimensional topography image of the lateral heterostructure withsuperimposed STS mapping at a sample bias of −1 V. The relativeelectronic DOS between borophene and PTCDA is in agreement with FIG.15C. The degree of interfacial electronic interaction is furtherexplored by a series of STS spectra taken across both the Ag/boropheneand PTCDA/borophene interfaces with lateral displacements of 3.0 Å and3.8 Å between adjacent points in FIGS. 15E and 15F, respectively. InFIG. 15E, far from the interface, both borophene and Ag(111) showcharacteristic bulk properties. A small upshift (−0.05 eV) of the Agsurface state feature to higher energy is observed when approaching theinterface from Ag(111). The transition in the STS spectra from PTCDA toborophene is abrupt and takes place within 1-2 nm in FIG. 15F, similarto the size of a PTCDA molecule. A small downshift of ˜0.15 eV of theLUMO+1 state is observed when approaching the junction from PTCDA,likely due to the weak van der Waals interactions between the junctionof PTCDA molecules and borophene. Compared, for instance, to theadditional features in the STS spectra of single layer MoS₂ and thelarge transition distance due to the presence of edge states andtransition regions at MoS₂ edges and grain boundaries, theborophene/PTCDA lateral heterojunction demonstrated through andrepresentative of this invention is surprising and unexpected in termsof its electronic abruptness at the single nanometer length scale.

In summary, representative self-assembled borophene/PTCDA lateralheterostructures with structurally and electronically abrupt interfaceshave been realized by sequential deposition of B and PTCDA on Ag(111).The borophene/PTCDA lateral heterostructures occur spontaneously, whichis consistent with molecular dynamics simulations that show that ahigher enthalpy of adsorption on Ag(111) and the lateral hydrogenbonding between adsorbed PTCDA molecules leads to preferential assemblyof PTCDA on Ag(111) compared to borophene. The weak chemical interactionbetween borophene and PTCDA is further corroborated by in situ XPSmeasurements. Molecular-resolution STM/STS shows that borophene/PTCDAlateral heterostructures are electronically abrupt with a transition inthe DOS from borophene to PTCDA occurring over the length scale of asingle PTCDA molecule.

EXAMPLES OF THE INVENTION

The following non-limiting examples and data illustrate various aspectsand features relating to the articles and/or methods of the presentinvention, including the assembly of boron allotrope orborophene/organic heterostructures, as are available through thesynthetic methodologies described herein. In comparison with the priorart, the present articles and methods provide results and data which aresurprising, unexpected and contrary thereto. While the utility of thisinvention is illustrated through the use of several articles, organiccomponents and substrates which can be used therewith, it will beunderstood by those skilled in the art that comparable results areobtainable with various other articles, organic components andsubstrates, as are commensurate with the scope of this invention.

Example 1

Growth of Borophene/PTCDA Lateral Heterostructures:

All growth is performed in a UHV preparation chamber (pressure <10⁻⁹Torr) that is directly connected to a loadlock, STM, and XPS system.Ag(111) thin films (˜300 nm thick) on mica substrates (PrincetonScientific Corp.) are cleaned by repeated Ar ion sputtering at 3.3×10⁻⁶Torr (30 min) followed by annealing at 550° C. (30 min). The depositionof boron is achieved by electron-beam evaporation (SPECS EBE-1) of apure boron rod (ESPI metals, 99.9999% purity) onto the cleaned Ag(111)substrates held at 480° C. The deposition flux is measured by the fluxelectrodes of the evaporator and is maintained at 20 to 28 nA with afilament current of −5.8 A and accelerating voltage of 1.3 to 1.6 kV.The typical deposition time is 20-30 min to achieve submonolayercoverage of borophene. The electron-beam evaporator is housed in aseparately pumped chamber with a base pressure of 8×10⁻¹¹ Torr, and theboron rod is degassed for >6 hr preceding evaporation. (The preparationand characterization of borophene and/or a boron allotrope comprising anelemental boron layer comprising a boron atomic thickness dimension isfurther described in co-pending application Ser. No. 15/430,885 filedFeb. 13, 2017, at but not limited to paragraph [0049] therein anddiscussions related thereto, the entirety of such co-pending applicationis incorporated herein by reference.) The deposition of PTCDA isachieved by thermally evaporating pure PTCDA molecules (Sigma-Aldrich,97% purity) in an alumina-coated crucible (R. D. Mathis) in the loadlockchamber (2×10⁻⁹ Torr) with a heating current of 4.8 Å. The molecules aredegassed overnight at 2.5 Å preceding evaporation. After ramping thecurrent to 4.8 Å over 6 min, an exposure time of 1 min results inmonolayer coverage on Ag(111) substrates, which are maintained at roomtemperature during deposition.

Example 2

Scanning Tunneling Microscopy and Spectroscopy:

A home-built UHV STM (˜10⁻¹⁰ Ton) is used for STM/STS characterizationat room temperature with a Lyding-design microscope. (See, E. T. Foley,N. L. Yoder, N. P. Guisinger, M. C. Hersam, Cryogenic variabletemperature ultrahigh vacuum scanning tunneling microscope for singlemolecule studies on silicon surfaces, Rev. Sci. Instrum. 75, 5280-5287(2004). However, conventional, commercially-available instrumentationcan be used with comparable effect.) The bias voltage is applied to thesample with respect to the electrochemically etched PtIr tip (Keysight).The piezo-scanner is calibrated against the Ag(111) lattice (x y) andatomic step height (z). Nanonis (SPECS) control electronics are used fordata collection. STS measurements are carried out with a lock-inamplifier (SRS model SR850) with 30 mV_(R)ms amplitude and ˜8.5 kHzmodulation frequency. Stable and reproducible spectroscopy was achievedfollowing tip conditioning that includes controlled touching of the STMtip to the Ag(111) surface. This process likely leads to the transfer ofAg atoms to the tip apex, which allows for reproducible room temperaturespectra on Ag(111), borophene, and PTCDA that are consistent withliterature reports.

Example 3

X-Ray Photoelectron Spectroscopy:

In situ XPS spectra are taken with an Omicron DAR 400 M X-ray source (AlKa), XVI 500 X-ray monochromator, and EA 125 energy analyzer in a UHVchamber (3×10⁻¹⁰ Torr) that is integrated with the STM system andpreparation chamber. The XPS energy resolution is 0.6 eV using apass-energy of 20 eV for core-level spectra. Modified Shirleybackgrounds have been subtracted using Advantage (Thermo Scientific)software. Given the trace amount of adventitious carbon for the cleanAg(111) surface (FIG. 16), all peaks are fitted after calibrating thespectra to the Ag 3d_(5/2) core-level peak (368.2 eV). This calibrationis validated by <0.04 eV changes of the raw Ag 3d_(5/2) peaks (FIG. 3)for clean Ag(111), borophene/Ag(111), and PTCDA/borophene/Ag(111) inconsecutive runs.

Example 4

Atomic Force Microscopy:

Ambient AFM characterization is carried out on an Asylum Cypher AFM intapping mode. Si cantilevers from NanoWorld (NCHR-W) are used with aresonant frequency of ˜300 kHz. The scanning rate is ˜1.5 Hz.

Example 5

Molecular Dynamics Simulations:

The Ag(111) substrate is represented by a hexagonally close-packedlattice of spherical beads with diameter and inter-atomic spacingGAg=2.898 Å. The coarse-grained PTCDA molecule is modeled through arigid, rectangular collection of 9×5 spherical beads (FIG. 10), designedbased upon the hydrogen bonding network and unit cell of theself-assembled herringbone structure (FIG. 6). The diameter of all PTCDAbeads is chosen as σ=1.61 Å (with a the LJ unit of length), so that thelateral dimensions of the modeled unit cell closely correspond to theexperimental dimensions. Only the beads capable of forming hydrogenbonds in self-assembled PTCDA molecules (FIG. 10) have an attractiveinteraction with the Ag atoms. This attraction is represented by a LJpotential, with effective length σ_(ij)=(σ_(i)+σ_(j))/2, whereσ_(ij)=σ_(Ag) or σ and cutoff of 5.635 Å (shifted to eliminate the LJpotential discontinuity). The adsorption enthalpy of PTCDA is varied bytuning strength of the LJ potential. All other units in a PTCDA moleculeinteract with the substrate via a purely repulsive LJ potential with thesame effective length and cutoff of 2.53 Å (again shifted to eliminate adiscontinuity in the potential).

Further details of the molecule modeling can be understood inconjunction with FIG. 10. As illustrated in FIG. 10, three hydrogenbonds form when the short end of a PTCDA molecule interacts with theside of another molecule. In the PTCDA model, two oxygen beads (purple)at the center of the short sides and four hydrogen beads (yellow) at thelong sides are assigned, and the attraction between a pair of oxygen(purple) and hydrogen (yellow) beads are used to represent the effectiveinteraction resulting from the three hydrogen bonds. Similarly, twohydrogen bonds form when the side of a PTCDA molecule interacts with theside of another molecule. Since this double bond can occur at foursides, another four oxygen beads (green) are assigned at the long sidesof the molecule, and the attraction between a pair of oxygen (green) andhydrogen (yellow) beads are used to represent one hydrogen bond. Thus,the six oxygen beads (green and purple) in the coarse-grained modelrepresent the oxygen atoms in the end groups of a PTCDA molecule, andthe four hydrogen beads (yellow) represent the hydrogen atoms at thesides of a PTCDA molecule. The attraction strengths for hydrogen beadswith purple oxygen and green oxygen beads are set to 5 k_(B)T and 5/3k_(B)T, respectively, giving each hydrogen bond strength of 5/3 k_(B)T,which is within the range of C—H . . . O hydrogen bond strength. Thecutoff for the LJ potential is chosen as 4.025 Å (2.5σ) and shifted toeliminate the discontinuity at the cutoff All other components in PTCDAmolecules interact via purely repulsive LJ potential with cutoff at1.807 Å (21/6σ, also shifted to eliminate the discontinuity). Theelectric quadrupole nature of PTCDA makes direct stacking of PTCDAmolecules unfavorable, which is modeled by placing four virtual beads inthe middle of the four sides of a PTCDA molecule. In the simulation, theaim is to probe the effect of heterogeneous substrates on the monolayergrowth of PTCDA molecules, thus the virtual bead sizes are chosen tosuppress multilayer growth. These virtual beads also account for therepulsive interactions between the negatively polarized anhydride groupsof two adjacent molecules, as well as the positively polarized perylenecores of two adjacent molecules, which prevent head-to-head and sideby-side assemblies, as experimentally observed. The two virtual beads onthe short sides only interact with each other via a purely repulsive LJpotential with σ1=5.796 Å. Likewise, the two beads on the long sidesonly interact with each other via the same potential with σ2=6.44 Å. Theinteraction strengths are set to k_(B)T and the interaction cutoffs areset to 21/6σ1 and 21/6σ2, respectively (shifted to eliminate thediscontinuity). The tuning of adsorption enthalpy is achieved by varyingthe interaction strength between silver atoms and the oxygen andhydrogen beads in PTCDA molecules.

For the study of self-assembly of PTCDA on heterogeneousborophene/Ag(111) substrates, 350 molecules are placed in a simulationbox with dimensions (231.84 Å)³ and periodic boundary conditions in thex and y directions. At the upper and lower z boundaries, purelyrepulsive LI walls are placed. The center of the Ag(111) substrate isplaced 1.61 Å above the lower z boundary and the center of the borophenelayer is placed 4.508 Å above the lower z boundary. For the study ofself-assembly of PTCDA on homogeneous Ag(111) substrates, 400 moleculesare placed in a simulation cell of the same size.

The LAMMPS package is used to perform the MD simulations. The equationsof motion are integrated using the velocity-Verlet algorithm. A Langevinthermostat is applied with temperature 1.0 ε/k_(B) and damping time 5τ,where ε and τ are the LJ units of energy and time, respectively. Thetime step is set to 0.01τ. Each simulation runs for a period of 1 to4×10⁶τ to reach equilibrium.

To calculate the relative Gibbs free energy ΔG(z), the center of asingle PTCDA molecule is placed at a distance z from the substrate (andcentered above a Ag atom), where z is varied from 11.914 Å to 2.254 Åwith step size 0.0805 Å. At each z, a canonical MD simulation isperformed with the center of mass of the molecule fixed to obtain theaverage force along the z direction (average forces along x and ydirections are confirmed to average out to zero) on the PTCDA molecule.Integration of this ensemble-averaged force with respect to distancefrom 11.914 Å to 2.254 Å yields the Gibbs free energy as a function of zwith respect to the Gibbs free energy of a molecule far from the surface(i.e., in free vacuum).

What is claimed is:
 1. A method of preparing a boron allotrope-organiclateral heterostructural article, said method comprising: providing anarticle comprising a substrate comprising a portion thereof coupled to aboron allotrope comprising an elemental boron layer; generating anorganic compound vapor from a solid organic compound source, saidorganic compound vapor having a higher enthalpy of adsorption on saidsubstrate compared to enthalpy of adsorption on said boron allotrope;and contacting said organic compound vapor with said article toselectively deposit said organic compound on a substrate portion notcoupled to said boron allotrope to provide a heterostructural articlecomprising said organic compound and said boron allotrope laterallyadjacent one to the other and providing a lateral interface one with theother.
 2. The method of claim 1, wherein said organic compound issubstantially absent on said boron allotrope.
 3. The method of claim 2,wherein said deposition provides complete structural and electronictransition from said boron allotrope to said organic compound layer overthe nanometric length scale of said organic compound.
 4. The method ofclaim 3, wherein said organic compound is PTCDA.
 5. A method of usingintermolecular hydrogen bonding to prepare a boron allotrope-organiclateral heterostructural article, said method comprising: providing anarticle comprising a substrate comprising a portion thereof coupled to aboron allotrope comprising an elemental boron layer; generating anorganic compound vapor from a solid organic compound source, saidorganic compound capable of intermolecular hydrogen bonding, saidorganic compound vapor having a higher enthalpy of adsorption on saidsubstrate compared to enthalpy of adsorption on said boron allotrope;and contacting said organic compound vapor with said article tointermolecularly hydrogen bond said organic compound and selectivelydeposit said organic compound on a substrate portion not coupled to saidboron allotrope to provide a heterostructural article comprising saidorganic compound and said boron allotrope laterally adjacent one to theother and providing a lateral interface one with the other, wherein saidorganic compound is substantially absent on said boron allotrope.
 6. Themethod of claim 5, wherein said deposition provides complete structuraland electronic transition from said boron allotrope to said organiccompound layer over the nanometric length scale of said organiccompound.
 7. The method of claim 5, wherein said organic compound isPTCDA.